WW2 RAF flying helmets

I'm embarking on research to do with flying helmets as worn by the RAF during WW2. My father, no longer alive, ran a leather goods business. During the war he manufactured 250,000 helmets for the RAF. I'm trying to find out the procurement story behind this; how companies tendered for business.

The business moved from London to Harrogate during WW2, which would fit with the Air Ministry decamping there, but haven't, so far, been able to find details of manufacture of helmets up there.

I was told that the Air Ministry was bombed during the war and therefore no records exist. Is this true?